Tissue engineering is a new field that has developed with the progress of science. Tissue engineering involves concepts and techniques from various fields of science such as life science, engineering, medical science and the like. Tissue engineering aims to understand the relationship between the structure and function of a body tissue and producing a substitute for a damaged body tissue or organ for transplantation purposes so as to maintain, improve or restore the function of a human body.
One typical tissue engineering technique comprises the following steps: removing a required tissue from a patient body; isolating a cell from the removed tissue; proliferating the isolated cell; seeding the cell in the biodegradable porous polymer scaffolds; culturing the cell in vitro for a predetermined period; and transplanting the obtained hybrid-type cell/polymer structure into the human body. After the transplantation is achieved, oxygen and nutrients are provided to the transplanted cells in biodegradable porous polymer due to the diffusion of bodily fluids until a blood vessel is newly formed. When the blood vessel is formed, the cells are cultivated and divided in order to form a new tissue and organ. During the formation of new tissue and organ, the polymer scaffolds become degraded and eventually disappear.
Accordingly, in the field of tissue engineering, it is important to prepare a biodegradable porous polymer scaffold that is similar to the body tissue.
In order to be used as a raw material for the polymer scaffolds, the material should properly serve as a matrix or frame so that tissue cells can adhere to the surface of the material and form a tissue in a three-dimensional structure. It should also serve as a middle barrier, which is positioned between a transplanted cell and a host cell. That is, it should be non-toxic and biocompatible such that neither blood coagulation nor inflammatory reaction occurs after the transplantation.
In addition, such material should be biodegradable so that as the transplanted cell properly functions as a tissue, it is completely degraded in vivo within a desired timeframe.
A biodegradable polymer, which is widely used as a raw material for the scaffold, includes polyglycolic acid (PGA), poly(L-lactic acid) (PLLA), poly(D,L-lactic acid) (PDLLA), poly(lactic-co-glycolic acid) copolymer (PLGA), poly(ε-caprolactone) (PCL), polyamino acid, polyanhydride, polyorthoester and their copolymers. However, only PGA, PLLA and PLGA have been approved from the U.S. Food & Drug Administration as biodegradable polymers, which may be used on human bodies. Further, they are used as raw materials for biodegradable porous polymer scaffolds for regeneration within human bodies.
Recently, various attempts were made to prepare a polymer having a porous structure through techniques such as: solvent-casting and particulate-leaching technique (see A. G. Mikos et al., Polymer, 35, 1068, 1994) wherein a single crystal NaCl is mixed, dried and dissolved in water; gas foaming technique (see L. D. Harris et al., Journal of Biomedical Materials Research, 42, 396, 1998) wherein a polymer is inflated by using CO2 gas; fiber extrusion and fabric forming process (see K. T. Paige et al., Tissue Engineering, 1, 97, 1995) wherein a polymer fiber is formed as a non-woven fabric to make a polymer mesh; thermally induced phase separation technique (see C. Schugens et al., Journal of Biomedical Materials Research, 30, 449, 1996) wherein a solvent contained in the polymer solution is immersed in a non-solvent to produce porosity; and emulsion freeze-drying method (see K. Whang et al., Polymer, 36, 837, 1995) wherein a polymer solution is mixed with water to form an emulsion, which is then frozen with liquid nitrogen and freeze-dried.
However, with the conventional methods, it is not easy to control the pore size of the scaffold. Further, the surface area and porosity of the resultant polymer scaffolds are comparatively low and the open structures are not formed well between the pores. In addition, they are disadvantageous in that there are occurrences of closed pores on the surface of the scaffolds, the process is comparatively complicated, the gas or toxic substance is secreted during the preparation of scaffolds, and there are remains of salt in the scaffolds.